There are four buildings. You start with the one with a blue sign on it. There you pull the block and slide down back to its entrance. Next, go to the building with the red sign. Climb the ledge and run upwards. The planks will break behind you, so if you need to repeat this you will have to climb the ice ledge in the building with the blue sign. Anyway, proceed this way, always watching your health since the Ice Guardian instantly fires at you. This way you will eventually reach the top of the red signed building where there is the hidden lab with Urgon's part inside.